JP2008300043A - Electrode for discharge tube, and cold-cathode fluorescent tube using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide with ease an electrode for a discharge tube with a low cathode fall voltage and excellent in emission efficiency, as well as a cold-cathode fluorescent tube using the same. <P>SOLUTION: The electrode for a discharge tube 1 is provided with a glass tube 2, and an electrode part 3. An electrode for a discharge tube 4 of the electrode part 3 is made of metal with a secondary electron emission coefficient of 1.5 or more or an alloy containing the metal. As the metal with a secondary electron emission coefficient of 1.5 or more, iridium (Ir) is used as an example. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode for a discharge tube and a cold cathode fluorescent tube using the same.

  A liquid crystal display (LCD) used in a display device such as a television receiver or a personal computer incorporates a backlight having a cold cathode fluorescent tube as a light source.

  Such a cold cathode fluorescent tube includes a glass tube portion and electrode portions provided at both ends of the glass tube portion (see, for example, Patent Document 1). The glass tube portion is sealed with a fluorescent paint applied on the inner surface and introduced with argon (Ar), neon (Ne), and mercury (Hg) for phosphor excitation as discharge gases. The electrode part is composed of a cup electrode, a sealing rod, and a lead wire. As a material for the cup electrode, nickel (Ni) has been conventionally used, and in recent years, niobium (Nb), molybdenum (Mo), tungsten (W) and the like are generally used.

  A cold cathode fluorescent tube emits light by glow discharge. Glow discharge is caused by ionization (α action) of gas molecules by electrons moving between the cathode and the anode and collision of Ar, Ne, and Hg positive ions with the negative electrode. Secondary electron emission (γ action) occurring in

In this glow discharge, the positive ion density of Ar, Ne, and Hg increases at the cathode descending portion, which is the discharge site on the cathode side, and a phenomenon occurs in which the voltage drops at the cathode descending portion (cathode falling voltage). Such a cathode fall voltage does not contribute to light emission, and as a result, increases the operating voltage and lowers the luminance efficiency. Here, the cathode fall voltage is related to the secondary electron emission, and depends on the secondary electron emission coefficient of the cold cathode material to be selected.
Japanese Patent Laid-Open No. 2005-285587

  In response to the recent market demand for longer-length cold cathode fluorescent tubes and higher luminance by driving with a large current, a cold cathode electrode having a low cathode fall voltage and a simple composition is desired.

  An object of the present invention is to provide a discharge tube electrode having a low cathode fall voltage and excellent luminous efficiency, and a cold cathode fluorescent tube using the same.

  The electrode for a discharge tube of the present invention is characterized by comprising a metal having a secondary electron emission coefficient of 1.5 or more or an alloy containing the metal.

  The present inventors use a metal having a secondary electron emission coefficient of 1.5 or more or an alloy thereof as an electrode for a discharge tube, thereby improving the electron emission property of the electrode and increasing the luminous efficiency with a low cathode fall voltage. It was found that can be realized easily.

  An example of the metal having a secondary electron emission coefficient of 1.5 or more is iridium (Ir) having a secondary electron emission coefficient of 1.5. Thereby, it is possible to easily realize that the cathode fall voltage is low and the luminous efficiency is increased. Further, iridium (Ir) or an alloy thereof can be composed relatively easily, and the electrode can be easily processed.

  Moreover, the present invention can provide a cold cathode fluorescent tube having a low cathode fall voltage and excellent luminous efficiency by using the discharge tube electrode having the above structure as a cold cathode.

  As shown in FIG. 1, the cold cathode fluorescent tube 1 of this embodiment includes a glass tube 2 and an electrode unit 3. The cold cathode fluorescent tube 1 has, for example, a straight tube shape having a diameter of about 4.0 mm and a length of about 300 mm.

  A phosphor 2 a is applied to the inner surface of the glass tube 2, and electrode portions 3 are attached to both ends of the glass tube 2. Further, the inside of the glass tube 2 is sealed in a state in which argon (Ar), neon (Ne), and mercury (Hg) for exciting phosphor are introduced as discharge gases.

  The electrode portions 3 provided at both ends of the glass tube 2 include a cup-type discharge tube electrode 4, a sealing rod 5, and a lead wire 6, and the sealing rod 5 is sealed with a glass coating layer 7.

  In the present invention, by using a metal having a secondary electron emission coefficient of 1.5 or more or an alloy thereof as the discharge tube electrode 4, the electron emission property of the electrode can be improved, the cathode fall voltage is low, and the luminous efficiency is increased. However, for this purpose, it has been found that it is effective to use iridium (Ir) or an alloy of iridium (Ir) and rhodium (Rh) or platinum (Pt) as the cup-type discharge tube electrode 4. did.

尚、カップ型の放電管用電極４は、直径が１．５ｍｍで、長さが約１５ｍｍとなっている。 Table 1 shows secondary electron emission coefficients of these metals and substances used as conventional electrode materials. Here, the secondary electron emission coefficient of iridium (Ir) is 1.5, the secondary electron emission coefficient of rhodium (Rh) is 1.15, and the secondary electron emission coefficient of platinum (Pt) is 1.44. The secondary electron emission coefficient of an alloy of iridium (Ir) and rhodium (Rh) (IrRh) with a weight ratio of rhodium (Rh) of 10 percent is about 1.5, and the weight ratio of platinum (Pt) The secondary electron emission coefficient of an alloy (IrPt) of iridium (Ir) and platinum (Pt) with 5% as the content is also about 1.5. Since any alloy has a small composition of rhodium (Rh) or platinum (Pt), it is almost equal to the secondary electron emission coefficient of iridium (Ir), which is the base material, and is about 1.5.

The cup-type discharge tube electrode 4 has a diameter of 1.5 mm and a length of about 15 mm.

  The enclosure rod 5 made of molybdenum (Mo) is sealed by a glass coating layer 7 made of Kovar glass, and a dimet wire is used as the lead wire 6 to be externally connected. Further, the discharge tube electrode 4 and the molybdenum (Mo) enclosure rod 5 are joined by laser welding. The molybdenum (Mo) enclosure rod 5 and the lead wire 6 as a dimet wire are joined by resistance welding.

  Next, the electrical characteristics of the cold cathode fluorescent tube 1 will be described with reference to FIGS.

  FIG. 2 is a graph showing the relationship between tube current and tube voltage of an alloy of iridium (Ir) and rhodium (Rh) (IrRh) and an alloy of iridium (Ir) and platinum (Pt) (IrPt). For comparison, the relationship between the tube current and the tube voltage of nickel (Ni) and molybdenum (Mo) that have been conventionally used as discharge tube electrodes is also shown.

  As shown in FIG. 2, when the discharge tube electrode 4 using these materials is used in the cold cathode fluorescent tube 1, when the tube current value is changed in the range of 4.0 mA to 8.0 mA, the tube voltage Decreases uniformly as the current value increases. At this time, by using the iridium (Ir) and rhodium (Rh) alloy (IrRh) having a large secondary electron emission coefficient and the iridium (Ir) and platinum (Pt) alloy (IrPt) discharge tube electrode 4, The tube voltage can be suppressed relative to (Ni) and molybdenum (Mo).

図３は、イリジウム（Ｉｒ）とロジウム（Ｒｈ）の合金（ＩｒＲｈ）、およびイリジウム（Ｉｒ）と白金（Ｐｔ）の合金（ＩｒＰｔ）の管電流―発光効率の関係を示すグラフである。尚、ここでも比較のため、ニッケル（Ｎｉ）およびモリブデン（Ｍｏ）の管電流‐発光効率との関係も併せて示す。 As described above, an iridium (Ir) and rhodium (Rh) alloy (IrRh) having a large secondary electron emission coefficient and an iridium (Ir) and platinum (Pt) alloy (IrPt) are employed as the discharge tube electrode 4. Thus, the cathode fall voltage that does not contribute to light emission can be suppressed. Specifically, as shown in Table 2, the values of the cathode fall voltage of these substances are about 10V to 20V with respect to nickel (Ni) and molybdenum (Mo) conventionally used as discharge tube electrodes, The cathode fall voltage can be reduced.

FIG. 3 is a graph showing the relationship between tube current and luminous efficiency of an alloy of iridium (Ir) and rhodium (Rh) (IrRh) and an alloy of iridium (Ir) and platinum (Pt) (IrPt). For comparison, the relationship between the tube current and luminous efficiency of nickel (Ni) and molybdenum (Mo) is also shown here.

  As shown in FIG. 3, when the discharge tube electrode 4 using these materials is used in the cold cathode fluorescent tube 1, the luminous efficiency is changed when the value of the tube current is changed in the range of 4.0 mA to 8.0 mA. Each gradually decreases as the current value increases. At this time, by using an alloy (IrRh) of iridium (Ir) and rhodium (Rh) having a large secondary electron emission coefficient and an alloy (IrPt) of iridium (Ir) and platinum (Pt) for the discharge tube electrode 4, High luminous efficiency can be obtained with respect to nickel (Ni) and molybdenum (Mo).

  As described above, an iridium (Ir) and rhodium (Rh) alloy (IrRh) having a large secondary electron emission coefficient and an iridium (Ir) and platinum (Pt) alloy (IrPt) are employed as the discharge tube electrode 4. Thus, even at 6.0 mA that normally flows in the driving state of a backlight or the like, the luminance efficiency can be increased, and even when the current value is increased (when the cathode current density is high), high luminous efficiency can be obtained.

  As described above, an alloy of iridium (Ir) and rhodium (Rh) (IrRh) and an alloy of iridium (Ir) and platinum (Pt) (IrPt) are used as the discharge tube electrode 4 of the cold cathode fluorescent tube 1. Thus, it is possible to easily provide a cold cathode fluorescent tube having a low cathode fall voltage and excellent luminous efficiency.

  In the present embodiment, in particular, a case where an alloy of iridium (Ir) and rhodium (Rh) (IrRh) and an alloy of iridium (Ir) and platinum (Pt) (IrPt) are used as the discharge tube electrode 4. Although described, the present invention is not limited to this, and iridium (Ir) alone may be used as the discharge tube electrode 4.

The figure which shows the structure of the cold cathode fluorescent tube of this embodiment. The graph which shows the relationship between the tube current-tube voltage of the cold cathode fluorescent tube of this embodiment. The graph which shows the relationship between the tube current-luminescence efficiency of the cold cathode fluorescent tube of this embodiment. DESCRIPTION OF SYMBOLS 1 ... Cold cathode fluorescent tube, 2 ... Glass tube, 2a ... Phosphor, 3 ... Electrode part, 4 ... Electrode for discharge tubes, 5 ... Enclosing rod, 6 ... Lead wire, 7 ... Glass coating layer.

Claims (3)

  An electrode for a discharge tube comprising a metal having a secondary electron emission coefficient of 1.5 or more or an alloy containing the metal. The discharge tube electrode according to claim 1,
An electrode for a discharge tube, wherein the metal is iridium (Ir).   A cold cathode fluorescent tube comprising the discharge tube electrode according to claim 1 as a cold cathode.

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